title: Challenges of using primary care electronic medical records in the UK to study medications in pregnancy.
abstract: OBJECTIVE
  This paper aimed to assess the prescription of medications during pregnancy by primary care physicians in the UK.
  
  
  METHODS
  We identified both completed pregnancies and pregnancies losses (ectopic pregnancies, miscarriages, terminations, and stillbirths) in women aged 13-49 years enrolled in The Health Improvement Network (THIN) between 1996 and 2010 following an algorithm with three sequential cycles that searched for Read Code groups in hierarchical order: (1) indicators of conception; (2) delivery or pregnancy loss; and (3) other codes suggestive of pregnancy. Completed pregnancies were linked to liveborn infants by means of the family identification number and date of birth. Prescription of specific drugs during the first trimester and time trends during the last decade were calculated.
  
  
  RESULTS
  A total of 191 000 pregnancies were identified, including 148 544 completed pregnancies and 42 456 (22.2%) pregnancies losses (ectopic pregnancies, miscarriages, terminations, and stillbirths). Of the completed pregnancies, 131670 (88.6%) were successfully linked with the offspring. The most commonly prescribed drugs were antibiotics, antimycotics, asthma/allergy medications, and analgesics. From 1996 to 2010, the proportion of completed pregnancies with at least one prescription during the first trimester increased for antidepressants (1.8% to 4.2%), thyroid hormones (0.7% to 1.6%), and opiods (1.5% to 2.6%), among other drugs.
  
  
  CONCLUSIONS
  In conclusion, the prescription of several medications by primary care physicians during the first trimester of pregnancy has risen in the UK during the last decade. We discuss how, when important challenges are considered, THIN may be a promising resource to study specific therapies during pregnancy.
authors.affiliation: Spanish Centre for Pharmacoepidemiologic Research (CEIFE), Madrid, Spain. luciaceife@gmail.com
authors.forename: Lucia
authors.initials: L
authors.lastname: Cea-Soriano
authors.forename: Luis A
authors.initials: LA
authors.lastname: García Rodríguez
authors.forename: Oscar
authors.initials: O
authors.lastname: Fernández Cantero
authors.forename: Sonia
authors.initials: S
authors.lastname: Hernández-Díaz
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D011307:Drug Prescriptions / Q000706:statistics & numerical data*; D017723:Drug Utilization Review / Q000379:methods* / Q000706:statistics & numerical data / Q000639:trends; D057286:Electronic Health Records / Q000706:statistics & numerical data*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D010818:Practice Patterns, Physicians'; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D055553:Prescription Drugs / Q000008:administration & dosage; D011320:Primary Health Care / Q000379:methods* / Q000706:statistics & numerical data / Q000639:trends; D006113:United Kingdom; D055815:Young Adult
chemical_list: D055553:Prescription Drugs
keywords: THIN; medication; pharmacoepidemiology; pregnancy; treatment patterns